We are continuing our studies of the biochemical mechanisms underlining the formation of myelin. We are concentrating on the synthesis of sulphatide, the sulphate ester of galactocerebroside, as a marker for myelin formation. We are pursuing these investigations on three different levels, 1) characterization of the enzyme involved in the formation of sulphatide, 2) the localization of this enzyme in oligodendroglia during myelin formation and 3) studies of the sequential changes in the myelin membrane as it is formed. Our results to date indicate that sulphatide is synthesized primarily in oligodendroglia. However, there is some synthesis in neurons and astroglia. The enzyme in the different cell types appears to be the same enzyme. There do appear to be sequential changes as the plasma membrane of the oligodendrocyte becomes myelin. It is possible to isolate a "myelin-like" or "premyelin" membrane which has a different lipid and protein composition that mature myelin. In our present studies we are attempting to correlate the appearance of the enzymes involved in myelin formation with morphological changes in the developing oligodendrocyte.